Mortar and pestle



pt- 1959 J. G. ASPLIN 2,903,198- MORTAR AND PESTLE Filed Dec. 6, 1957 A 'III III.

INVENTOR JAMES B. ASPLIN ATTORNEYS United States Patent 2,903,198 MORTAR AND PESTLE James G. Asplin, Waunakee, Wis., assignor to Wisconsin Alumni Research Foundation, Madison, Wis., a corporation of Wisconsin Application December 6, 1957, Serial No. 701,064 2 Claims. (Cl. 241-199) My invention relates to crushing and grinding and in particular provides a machine-driven mortar and pestle.

My invention is particularly adaptable for use in grinding dried soil samples and is of special value where many soil samples are to be prepared for soil analyses and the conventional hand operated mortar and pestle are obviously inadequate. Prior attempts to solve this problem by a machine-driven grinding device have proven unsatisfactory, primarily due to the dusting problem and the inability to maintain just adequate pressure between the grinding surfaces to crush the lumps and granules but not so much as to break down or grind the individual soil particles existing largely'as mineral crystals. In many types of soil analyses, particularly those relating to soil reaction and availability of various plant nutrients, and also certain types of mechanical analyses, it is essential that only the lumps and granules be pulverized and the individual grains or mineral crystals be not broken down or ground. In certain other types of analyses grinding of the discrete particles to a very fine powder is desirable, and this is possible by increasing the pressure between the grinding surfaces and prolonging the process.

It is thus a principal object of my invention to provide a grinding device of the mortar and pestle type which is peculiarly adapted to rapidly reduce the granule size of the soil samples, and the like, eg limestone, coal, etc., with a minimum of dusting and with control of the desired grinding pressure. It is a further object of my invention to provide such a grinding device of basically simple construction which allows complete view of the sample during the grinding process, and instant stoppage so as to make possible elimination of extraneous material, or withdrawal of the mortar for hand pestling if desirable for some reason, and at all times application of just the grinding pressure needed, and which can be easily cleaned to facilitate rapid changeover from one grinding operation to the next. It is also an object of my invention to provide a grinding device capable of handling reasonable volumes of material to be ground all of which becomes thoroughly mixed during the grinding process. It is still another object of my invention to provide such a grinding device which can be driven by conventional and readily available power equipment, such as a drill press. A special feature of this type of grinding mechanism (conventional mortar with novel power driven pestle) makes possible batch dumping of ground material into an easily attached and operated screening device.

These and other objects of my invention which will become more apparent hereinafter are essentially obtained by providing a mortar with a grinding surface in its bottom which receives a pestle similarly provided with a grinding surface on its bottom and which is provided with one or more fins which are inclined and contact the upper inner surface of the mortar such that when the pestle is rotated with the grinding surfaces spaced closely together the fins wipe downwardly along the inner walls of the mortar to carry the sample to be ground between the grinding surfaces. Of course, some of the material being ground must also escape upwardly so that there is a general movement of material from between the side walls of the mortar and pestle t0 the space between the 2,903,198 Patented Sept. 8, 1959 grinding surfaces and then back. The same wiping action also greatly reduces dusting which is otherwise intolerable with a high speed rotary grinding device having an open upper end.

For a more complete understanding of the practical application of the principles of my invention reference is made to the appended drawings in which:

Figure 1 is an elevation view, taken partly in section, illustrating a grinding device of my invention in open position;

Figure 2 is a fragmentary view similar to Figure 1 showing the operative relationship of the mortar and pestle in closed, grinding relationship; and

Figure 3 is another view of the device as shown in Figure 2 as seen from section line 33 in Figure 2.

Referring more particularly to Figure l, the reference numeral 10 generally designates the grinding device of my invention while the reference numeral 11 designates a conventional drill press employed to drive grinding device 10. conventionally drill press 11 houses a motor for rotating a chuck 12 about a vertical axis. Drill press 11 also includes a conventional rack and pinion movement permitting adjustment of the vertical position of chuck 12 by means of an external, rotatable handle 13. T

Grinding device 10 includes a mortar 14 which is mounted on the work table 15 of drill press 11 by supports in the form of trunnions 15a for tilting mortar 14 to empty it through an aperture 15b in work table 15. Screening equipment can thus be located beneath the work table for sorting and classifying the ground solids. Mortar 14 is of conventional design and includes a bottom 16 having a grinding surface 17 on its upper face, an integral lower side wall portion 18 of generally conical shape which extends upwardly from bottom 16 with its smaller end adjacent to bottom 16 and an integral, cylindrical upper side wall portion 19 which extends upwardly from the upper, larger end of conical side wall portion 18. The upper end 20 of upper side wall portion 19 of mortar 14 is open providing access to the interior of mortar 14, and grinding surface 17 curves upwardly and outwardly as the inner surface of conical side wall 18 merges smoothly into the inner wall of side wall portion 19.

Grinding device 10 also includes a pestle 21 whose grinding surface fits the grinding surface of the mortar and includes a bottom 22 having a curved grinding surface 23 on its under side and carrying a boss 24 on its upper side in which the lower end of an upwardly extended, vertical shaft 25 is fixedly secured by welding or other suitable arrangement. The upper end of shaft 25 is held fir-mly in chuck 12 of drill press 11. Pestle 21 also includes an integral lower side Wall portion 26 which extends upwardly from bottom 22 Widening into an integral upper cylindrical side wall portion 27 which extends upwardly from side wall portion 26. The outside transverse dimensions of upper side wall portion 27 of pestle 21 are substantially less than the transverse dimensions of inside of wall portion 19 of mortar 14. The height of upper side Wall portion 27 is, however, substantially identical with the height of upper side wall portion 19. The height of lower side wall portion 26 of pestle 21 is just slightly less than the inside height of lower side wall portion 18 of mortar 14, and the outside transverse dimension of bottom 22 of pmtle 21 is substantially smaller than the inside transverse dimension of bottom 16 of mortar 14. Thus when pestle 21 is introduced into mortar 14 to bring their grinding surfaces 17 and 23 in close relationship there exists a substantial space between the corresponding side wall portions of mortar 14 and pestle 21.

Pestle 21 is also provided with a plurality e.g. three fins 28 which are spaced at equal arcuate intervals withmaking abouttwo thirds of a revolution, has its upper end 29 located .at approximately the upper end of side wall portion 27, extends downwardly along upper side wall portion 27 and lower side wall portion 26 and terminates at its lower end 30 adjacent to grinding surface 23 on the bottom of pestle21. .Suitably Jfins 28 are welded to pestle 21 but alternatively the entire unit including pestle 21 and fins 28, which form a part of pestle 21, can be cast as an integral unit.

The outer peripheral edges 31 of fins 28 are in continuous contact with the inner surfaces of side wall portions 18 and 19 of mortar 14. It will be further noted that the portions of the edges 31 of fins 28 which contact the inner surface of lower side wall portion 18 of mortar 1 4function to hold grinding surfaces 17 and 23 at the optimum distance apart for the particulate size of ground product which is desired.

As noted above mortar 14 is mounted on supports in the form of trunnions a. The trunnions form a horizontal axis intersecting the vertical axis of the pestle during grinding operations to permit emptying of mortar '14. More specifically, two 'trunnions 15a are fixedly mounted on table 15 on opposite sides of aperture 15b androtatably receive stub axles 35 and 36 projecting from opposite sides of upper wall portion 19 or mortar 14. Stub axle 36, as it extends through its associated trunnion 15a, is bent into a crank arm 37 to facilitate manual rotation of mortar 14 about horizontal axles 35 and 36 while emptying mortar 14 through aperture 15b.

Beneath table 15 a hopper 32 is suspended for receiving materials emptied from mortar 14 through aperture 15b. A particle size classifying screen 33 is positioned across the inside of hopper 32 and is provided with a cam operated shaker of conventional construction which is externally driven by rotation of a shaft 34.

In operation handle 13 of drill press 11 is rotated clockwise to raise chuck 12 .and hence pestle 21 clear of mortar '14 (see Figure 1). A sample of material to be ground is then placed on the bottom 16 of mortar 14. The motor of drill press 11 is then started causing pestle 21 to rotate at a high speed clockwise in the illustrated case such that fins 28 rotate in a direction causing their peripheral edges 31 to appear to descend as seen in Figure 1. Handle 13 is then rotated counterclockwise to lower pestle 21 into mortar 14. As pestle 21 bottoms in mortar 14 (see Figure 2) it is mainly below the horizontal axis of trunnions 15a with its lower grinding surface 23 spaced just above grinding surface 17 in bottom 16 of mortar 14, some of the material to be ground is displaced upwardly into the space between the side walls 18 and '19 of mortar 14 and side walls 26 and 27 of pestle 21. The grinding operation which ensues between the relatively rotating surfaces 17 and 23 rapidly reduces the material contained therein to the desired condition. The downward wiping action exerted by fins 28 on material which is displaced into the side space between mortar 14 and pestle 21 produces a circulation of material from such space to between the grinding surfaces and a circulation of ground material back into the space be tween the side wall portions. The fine dust which is thus formed, however, is prevented from escaping by constant downward wiping action of fins 28 on walls 18 and 19. The grinding pressure can be readily controlled by handle 13 and after using the apparatus for a short time the operator can tell by the feel on handle when the grinding operation is complete and the sample is ready to be screened. At any time during the grinding operation a complete view of the sample can be readily obtained by raising the pestle by rotating handle 13 clockwise. When the material has been finely ground to the desired consistency, the drive motor of drill press 11 is turned off and handle 13 rotated to raise pestle 21. The ground sample is then removed from mortar 14 by pulling crank 37 forward to tile mortar 14 and dump the ground material through aperture 15b into hopper 32 in which the ground material is classified by screen 33, assisted by shaking if desired.

Although I have described only one embodiment of my apparatus many variations will be readily apparent to those skilled in the art. In some circumstances it can be more desirable to make the grinding surfaces flat rather than curved as shown; only a single fin 28 may be required under other circumstances; raising and lowering of the pestle is not entirely necessary since material to be ground can be fed in between the mortar and pestle at their upper ends and ground material removed by providing a suitable port at the center of bottom 16 for removal of ground solids. As suggested above it is advantageous to arrange mortar '14, when batchwise operation is contemplated, such that mortar 14 can be tilted to empty its contents in between grinding operations. Where 'the material is sorted -or classified after grinding by screening as illustrated, vacuum devices can also be employed to remove dust during this operation.

'I claim:

1. A grinding device for grinding material which includes a mortar having a bottom provided with a grinding surface on the upper side thereof, and a side wall portion extending upwardly from said bottom defining .an opening in the :upper end of said mortar providing access .theret'hroug'h to the grinding surface on said bot- .tom of said mortar; a pestle having a bottom provided with a grinding surfacelon the under side thereof, a side wall portion extending upwardly from said bottom, a plurality .of .thin fins uniformly afiixed around said side wall portion of said pestle each having the same .pitch extending spirally aboutsaid pestle and perpendicularly outwardly therefrom with adecreasing outstanding extent from top :to bottom, one end of said fin terminating adjacent to the upper end of said pestle and the second ,end of said fin terminating adjacent to the bottom grinding surface of said pestle and spacing said pestle from the bottom of said mortar, :said pestle being positionable through the open upper end of said mortar to bring said grinding surfaces of said mortar and said pestle into a closely spaced apart grinding relationship with the outer surface of the side wall portion of said pestle spaced from the inner surface of said side wall portion of said mortar defining a material receiving zone therebetween and with the peripheral edges of said fins in continuous contact with the inner surface :of said side wall portion of said mortar; means for moving said pestle from a position above said mortar into said position in said mortar; and means for rotating said pestle in said mortar about a vertical axis to rotate .said grinding surfaces relative to each other and in a direction causing the peripheral edges of said fins to wipe downwardly with respect to the inner surface of said side wall portion of said mortar to carry material in said material receiving zone between said relatively rotating grinding surfaces.

2. A grinding device according to-clairn l in which said mortar is mounted with supports for rotation about a horizontal axis to permit emptying of said mortar, the horizontal axis of the supports intersecting the vertical axis of the pestle during grinding operations when the pestle is located mainly below said horizontal axis.

References Cited in the file of this patent UNITED STATES PATENTS 399,809 White Mar, 19, 1889 512,635 Traver Jan. 9, 1894 870,087 Dickins Nov. 5, 1907 1,369,209 7 Wright Feb. 22, 1921 FOREIGN PATENTS 23,760 Great .Britain of 1895 

